I. Field of the Invention
The invention relates to an apparatus for the timed transporting of forms, preferably continuous forms, over the writing beam of a printing device, with a transporting device mounted at the delivery end for the forms and causing the forms to advance at timed intervals, and with a braking device mounted at the entry end for the forms and serving to hold the form taut on the writing beam.
II. Description of the Prior Art
In known apparatus for the kind described above, the form is pulled away from a pile located below and drawn around a roller-shaped writing beam, forming looping angles of up to 180.degree.. Transporting is effected by means of a form transporting device mounted downstream of the writing beam at the delivery end for the forms, e.g. by means of a set of spiked belts. Transporting devices of this kind are known by the name "Leporello". At the entry end upstream of the writing beam is mounted a paper brake which ensures that the forms, particularly multiple sets of forms, abut on the writing area under mechanical tension. In these known constructions, the breaking elements are constantly pressed against the form by springs or, alternatively, under their own weight. Braking devices of this kind with a static effect have proved unsatisfactory, inasmuch as even small braking forces cause relatively high tensile stresses in the transporting of the forms when they loop round the writing beam, owing to the friction of the loop, and in many cases this results in the tearing of the transporting perforations. Moreover, when multiple sets of forms are being transported round the writing beam, the stitching comes undone and the transporting perforations move out of alignment, which may result in these perforations becoming detached, for example, from the spikes of the set of spiked belts. Furthermore, the different circumferential lengths of the inner and outer sheets of forms in a multiple set, when there is a large looping angle about the writing beam, causes the inner form sheets to buckle between the stitching, and, when the forms are being transported under tension, this together with the friction of the loop acting on the inner form sheets can result in breakage of the stitching.
On the other hand, however, it is essential for the writing or printing operation that the form sheets be securely held and stopped on the writing beam, since the printer exerts forces which act backwards and forwards on the form and could cause harmful movement or slipping of these forms if they were not adequately held.